28 June 2012

Balloon-borne camera, part 5: balloon choice, and first flight!

We've connected the picavet to the line, so now we're ready to fly! Now we need balloons. How many, though?

(Apologies in advance for the lack of pictures at the beginning of this post, there will be awesome pictures and video later)

21 June 2012

Balloon-borne camera, part 4: Connecting the kite line

Last time, we strung the picavet and had it ready to hang from the kite line. This quick post will show you how I did it.

First, it's important to mention that in kite aerial photography, which we're assuming is basically equivalent to our balloon photography, it's much preferable to hang the camera rig from the kite line than from the kite (or balloons) itself. This is because the kite line jerks around less than the kite, so the camera stays more stable and you can get a better picture.

There are special hooks for attaching a the rig to a kite line, like these "hangups" (scroll down about halfway), but I went for the don't-order-anything option and tied some non-slip loops in the kite line (EDIT: knots in the line are a weak point, and can lead to line failure. Here's a better solution). Here's a photo with a ruler for scale. The loop on the end of the line is for attaching the balloons.

The spool of kite line is on the right. Moving right are two loops for attaching the camera rig, about 20 cm apart. The loops were made by tying a bowline-on-a-bight into the kite line.
And there you have it! Now you clip the camera rig onto the loops, and viola! You're ready to hook up your balloons.
Carabiners (I switched back to those) clipped through the loops in the kite line. The picavet is hanging below, out of shot.
Next time: lifting everything into the air!

18 June 2012

Balloon-borne camera, part 3 - Stringing the picavet

If you're following from last time, you should now have assembled your picavet cross. Now we need to hang it from the kite line! We do this using a few meters of string and running it through the eyes on the picavet and through some connectors that we will tie on to the kite line (i.e. the keychain carabiners I mentioned in the last post). You'll need to tie some knots - I recommend netknots.com as very helpful.

The process looks like this:

I constantly referred back to this animation while I strung my picavet.

The first thing I did was to cut about 6 armlengths of the string. I had a really frustrating time keeping such a long length from getting hopelessly tangled, so my advice is to hold on to the ends at all times. This should prevent tangles.

I laid out my parts like this:

A short apology - for this version of my picavet, I decided to replace the carabiners with 2 card rings. Since the string goes through each kite line attachment point twice, I thought this might prevent the string from rubbing on itself while in flight. We'll see if there's any difference. Key rings could also work.

You can see that I took one end of the string and tied it to the card rings on the right. This was just to keep it in place while I did the rest of the stringing.

The rubber bands are there in case I decide later to use them to hold the camera - you can't slip them on once the stringing is finished. Rubber bands aren't a very safe way to hold the camera in place, but they are easy to slip on and off the camera if you're doing a lot of testing and the camera isn't going to go very high. I actually found it very helpful to record some footage while just tying the kite line to a coat rack in my office and hanging the picavet and camera from that as I moved the kite line up and down.

Also notice (1) the central washer in the middle of the picavet cross, and (2) all the eyes are facing the same direction!

Using the animation above, I began threading the string. Here are some photos of that.

(1) One end of the string is tied to the card rings.

(2) Hanging on to the loose end, I dumped the string off my desk to free space. The central washer is held down with a heavy magnet as I thread the string through.

(3) Through the first loop of the second set of card rings and back...

(4) Through the right eye...

(5) Through the left eye!

When you've gone through the last eye, hold the free end of the string while untying the other end. I used a double fisherman's knot. Then, tie the ends together and cut off excess string. You're done!

It definitely took me a couple tries to get it right. The more I tried, the easier it was to understand how the picavet is supposed to be strung. Even if my instructions and pictures aren't very clear, really the best way to string the picavet correctly is just to try it a couple times until the method begins to make sense.

Here is the final product!

The next post will be short and sweet, about connecting the picavet to the kite line.

13 June 2012

Balloon-borne camera, part 2 - Building a stable camera platform

As I mentioned in my last post, the major problem we were having was how to stabilize the camera so you could get a decent video of it. A little searching online led me to kite aerial photography enthusiasts, who prefer the picavet as a way of suspending a camera from the kite line so that the camera naturally levels itself. I decided to construct one and see if it gave us any better results.

Two websites were particularly helpful to me and deserve special mention - Charles Benton's Kite Aerial Photography page and the KAPER Picavet page. This last one in particular had useful images and diagrams.

Briefly, a picavet is basically a cross suspended from the kite line (not from the kite itself) by a rope strung through the four corners of the cross. Each corner has an eye through which the rope runs, along which the picavet can slide. The camera is attached to the picavet from below. This rig uses its own weight to slide down to the bottom of the rope, where it hangs perpendicular to the ground. It continuously readjusts itself as the kite line moves. The principle on which it works deserves its own post, so I'll leave it at that for now.

This diagram from the KAPER site shows the major parts:

Picavet diagram. Points A and B attach to the kite line. The camera hangs underneath the cross.

We wanted to take a very low-budget approach using materials found around the museum. This picture shows some of what I collected:

String, washer, balsa wood, and glue gun
Cup hooks

On the top starting from the left, you see a spool of reasonably strong string (I can snap it by pulling, but I have to pull really hard), a tiny washer, two rectangular sticks of balsa wood (30 cm x 2 cm), and a hot glue gun. Other materials included some E-Z hang cup hooks for hanging things from walls (bottom), and (not shown) pliers and two cheapo carabiners like the ones you get in the checkout aisle at a convenience store.You'll see the pliers and carabiners in later pictures.

Note: If you plan on lifting a fancy camera that will be expensive to replace, I really suggest you use stronger materials, like aluminum for the cross, bolts to connect the cross pieces, sturdy kite line for the string, and real climbing carabiners. My approach works well for our 30 g picavet and 30 g camera, but doesn't really scale.

Alright, now we're ready to put it together. The first step is to make the cross out of balsa wood. I used a ruler to mark the center of each piece, and did my best to align them perpendicularly. I drew lots of guide lines on the wood to help me. Carefully holding the pieces in place, squirt glue from the glue gun down the edges where the pieces meet (all four edges - flip the cross over to get the last two). There are probably more secure methods of joining the cross-pieces, but this one works well enough for our light load and is quick and simple to do. Feel free to substitute your own glue, but I would be very hesitant to use arts and crafts glue. Stick to stuff meant for hardware, like cyanoacrylate-based adhesives.

The last step is to screw the cup hooks into each end of the cross. Before you do that, you need to close the hooks so that the end makes an eye (obviously, an alternative is to simply use eye bolts instead of hooks, but I used what I was able to most easily find). Just crush the hooks with pliers, like in the following two pictures. Crush them and crush them well, so the string won't slip out later when your camera is 50m in the air (you can also avoid this by using thicker string or rope).

Not crushed.

Screw one into each end of the picavet cross. When you're done, turn them all to face the same direction. It should look something like this:
Picavet cross, with eyes oriented left-to-right. You can also see where I glues the cross pieces together. Ignore the hole in the middle - that was a failed experiment! I promise to explain it later.
On a final note, feel free to replace these materials with anything else you feel is better or easier for you to obtain. Eye bolts, for example, would have been a good replacement for the cup hooks, but I found the cup hooks first so that's what I went with.

Congrats, the base of the picavet is finished! Next time: stringing it and hanging it from the kite line.

Disclaimer: Although I am a volunteer at the Canada Science and Technology Museum, the content on this blog in no way reflects an official communication of the museum. 

11 June 2012

Balloon-borne camera, part 1 - Introduction

One of my projects for the Canada Science and Technology Museum (/Musee de la Science et de la Technologie du Canada) is to get their balloon-borne camera project working. This is going to be a summer camp activity where the campers use balloons to lift a camera high into the air and record some video. If you're coming here to find out how it was built, welcome! You're the reason for these posts, and I hope you find them useful. I'll just warn you that this will be more of a story than a how-to - I will probably have quite a few mistakes, dead-ends, and corrections as I go along. I'll do my best to update my posts when this happens, so you can skip ahead to working solutions.

The first attempt was the most straightforward - we hung the camera from underneath about 15 balloons. Here's the video from that first try:

As you can see, the camera had a tendency to swing pretty wildly. We chose the particular camera (a Digital Concepts 3-in-1 Micro Digital Camcorder) because we're still testing out the project and if we lost the camera it wouldn't hurt our wallets too badly. So, we aren't expecting HD quality video, but still we should be able to get a better video than that. It looks like the major problem is stability - we need to find a way to stop the camera from swinging.

 Where do I turn to when I need help? The internet! I discovered after some searching that this project is quite similar to kite aerial photography, an activity with a very active online presence. In KAP, as the name suggests, you use a kite instead of balloons to lift your camera into the sky. Apparently this technique is very popular with archaeologists who need a quick, inexpensive, and relatively uncomplicated way to get overhead photos of their dig sites. They have developed some nice tricks for getting good pictures.

Their preferred device for stabilizing a camera is called a picavet, developed shortly before the first World War by the French inventor Pierre Picavet. In the next post, I'll show (with lots of pictures!) how I built mine and explain how it works.

Disclaimer: Although I am a volunteer at the Canada Science and Technology Museum, the content on this blog is my own and only my own, and does not represent an official statement by the museum.

06 June 2012

Update: Poland is over, on to new things!

A brief update on my status, because I'm planning on actually writing over the next few weeks and I need something to bridge the gap between posts!

My time in Poland has come to an end. I finished my MC-PAD fellowship and successfully defended my thesis, making me a Master of technical physics with a specialization in nuclear (really, particle) physics. I really loved Poland, but at the same time I'm happy to be moving on to the next step with my career.

I'm excited to say that in the fall I'll be starting the physics PhD program at Johns Hopkins University, in Baltimore, MD! They're a top program and they made me a great offer, which came with the added bonus that I finally wouldn't be an ocean apart from my girlfriend.

In the meantime, Katie invited me to come to Ottawa with her for the summer, where she is working with the Canadian government in a US-Canadian partnership program. To stay occupied until August, I've offered my services to the Canada Museum of Science and Technology. They have given me some really cool projects to work on for the summer camps and various other events, and in return I'm learning a lot about communicating science to the public. 

This blog will hopefully document the progress of those projects (since they mostly involve building cool stuff). Look forward to pictures and video from the June 5 transit of Venus across the Sun (if you are unfortunate enough to be on my email lists, I'm sure you've heard enough from me about it already), and how to lift a video camera with balloons. That's what I'm working on now, and future projects will also be posted here.